1. Field of the Invention
The present invention relates to a fuel injection pump for diesel engines. Specifically, the present invention relates to a fuel injection pump equipped with deflectors at input/spill ports of a plunger barrel in order to prevent occurrence of cavitations when fuel is spilled through the ports to finish fuel injection by allowing high-pressure fuel spilled from the plunger room through the ports to impinge against the deflectors.
2. Description of the Related Art
In many of jerk fuel injection pumps for diesel engines, deflectors are provided at input/spill ports of the plunger barrel so that fuel spilled from the plunger room at high speed through the ports impinges against the deflectors in order to prevent impingement of the high speed fuel against the casing of the injection pump, since the impingement induces cavitation erosion on the inside surface of the ports and fuel gallery surrounding the ports.
FIG. 5 is a sectional view along the center line of a plunger of a jerk fuel injection pump for a diesel engine to which the present invention is applied.
In FIG. 5, a plunger barrel 102 is fixedly provided in a pump case 105. A plunger 100 is fit in the plunger barrel 102 to be reciprocated. The plunger 100 is driven to reciprocate by means of a fuel cam not shown in the drawing via a tappet 106 and tappet spring 107. A plunger room 111 is formed in the plunger barrel 102 above the top face of the plunger 100. Fuel fed from a fuel gallery 104 formed between the inner surface of the pump case 105 and outer surface of the plunger barrel 102 through the input/spill ports 103 into the plunger room 111 is compressed to a high pressure by moving the plunger 100 in an upward direction. The highly pressurized fuel pushes open a delivery valve 108 seating on a valve seat 110, and the highly pressurized fuel flows through an outlet passage 109 to a fuel injection valve not shown in the drawing.
Deflectors 10 are located at the fuel gallery side openings of the inlet/spill ports 103. When the spill groove 101 of the plunger 100 uncovers the inlet/spill ports 103, pressurized fuel in the plunger room outbursts through the ports 103 and impinges against the deflectors 10. Occurrence of cavitation erosion on the surface of the inlet/spill ports 103 and the fuel gallery 104 is prevented by the impingement of fuel against the deflectors 10.
Fuel injection pumps equipped with deflectors like this are disclosed in Japanese Laid-Open Patent Application No. 2000-179428 (patent literature 1) and Japanese Laid-Open Patent Application No. 9-144627 (patent literature 2).
In the fuel injection pump disclosed in the patent literature 1, the deflector for preventing cavitation erosion is shaped into a hexagonal socket head bolt having a protrusion to be inserted into the inlet/spill port with a plurality of fuel passages drilled to surround the socket part of the bolt to allow fuel that outbursts from the plunger room through the inlet/spill port to flow into the fuel gallery, wherein the deflector is screwed to the plunger barrel and further retained to the plunger barrel by means of a snap ring in order to prevent it from slipping out even when the screw has loosened.
In the fuel injection pump disclosed in the patent literature 2, the deflector is screwed to the pump case to face the inlet/spill port. Porous material is adhered on the end of the deflector facing the port to allow fuel bursting out through the port to impinge against the porous material, thereby alleviating rapid pressure change at the fuel impinging part and preventing occurrence of cavitation erosion.
In these prior art, the deflector is fixed securely to the plunger or pump case.